Ferroelectric liquid crystal panel

ABSTRACT

A liquid crystal display panel including first and second substrates, and a FLC layer interposed therebetween. A small quantity of additives are mixed in the FLC layer, without changing the electrical or chemical properties of the FLC. Under a proper temperature and an electric field, the FLC layer is ripened sufficiently. Thereafter, the FLC is exposed to light such that polymer networks are formed in the FLC layer due to the polymerization by the additives. The polymer networks connect with each other across molecular layers in the FLC such that the molecules of the FLC are stabilized in proper orientations and maintain their molecular layer structure regardless of the temperature variance. And, the diffraction grating becomes stable regardless of the temperature variance, and fast response time and good gray scale are achieved.

[0001] This application claims the benefit of Korean Patent ApplicationNo. 1999-0059463, filed on Dec. 20, 1999, which is hereby incorporatedby reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to liquid crystal panels for liquidcrystal display (LCD) devices. More particularly, the present inventionrelates to a liquid crystal panel that uses a ferroelectric liquidcrystal.

[0004] 2. Discussion of the Related Art

[0005] A conventional liquid crystal display (LCD) includes a displaypanel. A display panel typically has upper and lower substrates that areattached with each other, and an interposed liquid crystal, usually anematic, a smetic, or a cholesteric liquid crystal. A liquid crystaldisplay device utilizes the electro-optic effects of the liquid crystal.A display panel is operationally divided into a plurality of liquidcrystal cells. On the exterior surfaces of the upper and lowersubstrates, polarizers or retardation films are selectively attached.

[0006] A major design consideration of a liquid crystal cell is thecharacteristics of the particular liquid crystal that is used. A goodliquid crystal should have a fast response time, a good gray scale, anda wide viewing angle, all while operating at a low driving voltage.However, it is very difficult to find a liquid crystal that has all ofthose characteristics. Thus, various designs have been adopted forliquid crystal display devices.

[0007] Among the various types of liquid crystals, a low twisted nematic(LTN) liquid crystal has advantages of a short response time and a goodgray scale. However, it typically has low contrast ratios and relativelypoor color-dispersion properties. Other twisted nematic (TN) liquidcrystals have higher twist angles (such as 90 degrees) or employing anin-plane switching (IPS) mode. While those liquid crystals can provide awide viewing angle, afterimages are produced when displaying movingimages, and their brightness is relatively low. The anti-ferroelectricliquid crystal (AFLC), or the optically compensated birefringence (OCB),have advantages of a wide viewing angle and a fast response time,although there are problems with contrast ratios and cell gap control.

[0008]FIG. 1 is a cross-sectional view illustrating a conventionalTN-LCD panel 20. As shown in FIG. 1, the TN-LCD panel has lower andupper substrates 2 and 4 and an interposed liquid crystal layer 10. Thelower substrate 2 includes a substrate 1 having a TFT “S” that is usedas a switching element to change the orientation of the liquid crystalmolecules. The TFT “S” includes a pixel electrode 14 that applies avoltage to the liquid crystal layer 10 in accordance with signals thatare applied to the TFT “S”. The upper substrate 4 has a color filter 8for implementing color, and a common electrode 12 on the color filter 8.The common electrode 12 serves as an electrode for applying a voltage tothe liquid crystal layer 10. The pixel electrode 14 is arranged over apixel portion “P,” i.e., a display area. Further, to prevent leakage ofthe liquid crystal layer 10 between the substrates 2 and 4, thosesubstrates are sealed by a sealant 6.

[0009]FIGS. 2A to 2C illustrate various alignments of possible liquidcrystal molecules in the liquid crystal layer. As shown in FIG. 2A, inthe nematic liquid crystal, each rod-like molecule fluctuates quiterapidly, but the molecules have a definite orientational order expressedby a unit vector “

” called a director. As shown in FIG. 2B, in the smetic liquid crystalthe molecules have a layered structure in which the molecularorientation is perpendicular or nearly perpendicular to the layers. Asshown in FIG. 2C, in the cholesteric liquid crystal, the director

changes its orientation gradually along a helical axis. The helical axiscoincides with the optical axis of this material. Among the threedifferent types of liquid crystals, the nematic liquid crystal is mostwidely used in liquid crystal display devices.

[0010] Liquid crystals for liquid crystal display devices should:

[0011] a) have a liquid crystal phase that extends from low to hightemperatures, and thus are operable over a range of temperatures;

[0012] b) be chemically and optically stable over time;

[0013] c) have a low viscosity and a fast response time;

[0014] d) have highly ordered molecular alignments and thus provide agood contrast; and

[0015] e) have a large dielectric anisotropy and a low operatingvoltage.

[0016] The electro-optic effect enables electrical modulation of lightby changing the alignment of the liquid crystal molecules using anapplied electric field.

[0017] Among the various types of nematic liquid crystals, a twistednematic (TN) liquid crystal and a super twisted nematic (STN) liquidcrystal are often used. For a TN liquid crystal panel, a nematic liquidcrystal is interposed between transparent lower and upper electrodes(reference the common electrode 12 and the pixel electrode 14 of FIG.1). Those electrodes induce a definite molecular arrangement such that agradual rotation of the molecules occurs between the lower transparentelectrode and the upper transparent electrode until a twist angle of 90degrees is achieved. In an STN liquid crystal panel the angle of twistrotation is increased to 180 to 360 degrees.

[0018] The basic configuration and operation of a twisted nematic liquidcrystal display device will now be explained. As shown in FIG. 3A,opposed and spaced apart first and second polarizers 10 and 16,respectively, have perpendicular first and second transmittance axisdirections 40 and 42. Between the two polarizers 10 and 16 are first andsecond transparent substrates 12 and 14, which are also opposed to andspaced apart from each other. Spacers are used to maintain the cell gapbetween the substrates. For example, plastic balls or silica ballshaving a diameter of 4 to 5 micrometers can be sprayed on the firstsubstrate.

[0019] Still referring to FIG. 3A, the first and the second transparentsubstrates 12 and 14 include first and second orientation films 20 and22, respectively, on their opposing surfaces. Between the first andsecond orientation films 20 and 22 is a positive TN liquid crystal 18.

[0020] The positive TN liquid crystal 18 has a characteristic that itarranges according to an applied electric field. The first and secondpolarizer 10 and 16, respectively, transmit light that is parallel withtheir transmittance-axis directions 40 and 42, but reflect or absorblight that is perpendicular to their transmittance-axis directions 40and 42.

[0021] The first and second orientation films 20 and 22 were previouslyrubbed in a proper direction with a fabric. This rubbing causes thepositive TN liquid crystal molecules between the first and secondtransparent substrates 12 and 14 to become tilted several degrees. Firstand second rubbing directions 50 and 52 of the first and secondorientation films 20 and 22 are, respectively, parallel with thetransmittance-axis directions of the first and second polarizers 10 and16. With no electric field applied across the positive TN liquid crystal18, the orientation of the liquid crystal molecules twists between onesubstrate to the other at a definite angle, that angle being the twistedangle of the positive TN liquid crystal 18.

[0022] During operation, a back light device 24 irradiates white lightonto the first polarizer 10. The first polarizer 10 transmits only theportion of the light that is parallel with the first transmittance-axisdirection 40. The result is a first linearly polarized light 26 thatpasses through the polarizer 10. The first linearly polarized light 26then passes through the positive TN liquid crystal 18 via the firsttransparent substrate 12.

[0023] As the first polarized light 26 passes through the positive TNliquid crystal 18, the first polarized light 26 changes its phaseaccording to the twisted alignment of the positive TN liquid crystalmolecules. Accordingly, the first linearly polarized light 26 becomes anelliptically (possibly circularly) polarized light 28.

[0024] The elliptically polarized light 28 passes through the secondtransparent substrate 14, and meets the second polarizer 16. When theelliptically polarized light 28 passes through the second polarizer 16,the second polarizer 16 transmits only the portion of the ellipticallypolarized light 28 that is parallel to the second transmittance-axisdirection 42. A polarized light 30 is then emitted. In theabove-mentioned operation, a white state is displayed.

[0025] Turning now to FIG. 3B, when a voltage supplier 35 induces anelectric field through the positive TN liquid crystal 18, the positiveTN liquid crystal molecules rotate and arrange such that thelongitudinal axes of the molecules are perpendicular to the surfaces ofthe first and second substrates 12 and 14. Accordingly, the firstlinearly polarized light 26 passes through the first transparentsubstrate 12, the positive TN liquid crystal 18, and the secondtransparent substrate 14 without phase change. The first linearlypolarized light 26 then meets the second polarizer 16. As the secondpolarizer 16 has the second transmittance-axis direction 52 which isperpendicular to the first linearly polarized light 26, the secondpolarizer 16 absorbs or shields most of the first linearly polarizedlight 26. Thus, little or none of the first linearly polarized light 26passes through the second polarizer 16. Accordingly, a dark state isdisplayed.

[0026] Recently, a liquid crystal projector that uses theabove-mentioned TN liquid crystal panel has been developed, althoughresearch continues. The liquid crystal projector displays images formany users in a theater or in a meeting room. In that liquid crystalprojector, transmissive liquid crystal panels having TFTs are used aslight valves.

[0027] Referring to FIG. 4, the liquid crystal projector includes red,green, and blue dichroic mirrors 200 a, 200 b, and 200 c; red, green,and blue liquid crystal panels 220 a, 220 b, and 220 c; and a lens 240that concentrates and focuses light from the liquid crystal panels ontoan image screen 250 that displays images.

[0028] In operation, a light source (not shown in FIG. 4, but see FIG.12) irradiates white light onto the red dichroic mirror 200 a. Thatmirror reflects the red portion of the white light to the red liquidcrystal panel 220 a. The green and blue portions of the white light passthrough the red dichroic mirror 200 a to the green dichroic mirror 200b. The green dichroic mirror 200 b reflects the green portion of thewhite light onto the green liquid crystal panel 220 b. The blue portionof the white light is directed onto the blue liquid crystal panel 220 c.The red light from the red liquid crystal panel 220 a is reflected by afirst total reflection prism 230 a into the lens 240. The green lightfrom the green liquid crystal panel 220 b is reflected by a second totalreflection prism 230 b into the lens 240. The blue light from the blueliquid crystal panel 220 c is reflected first by a blue dichroic mirror200 c, and then by a third total reflection prism 230 c into the lens240. The lens 240 then concentrates and focuses its received light ontothe image screen 250 to display a composite color image.

[0029]FIGS. 5A and 5B illustrate the operation of a light valve. Asshown, first and second substrates 310 and 320 having first and secondpatterned electrodes 330 a and 330 b are spaced apart from each other,and a liquid crystal 300 is interposed therebetween. When no electricfield is induced by the first and the second patterned electrodes 330 aand 330 b, as shown in FIG. 5A, the liquid crystal 300 maintains itsfirst ordered molecular alignment wherein the liquid crystal moleculesare parallel with the substrates.

[0030] However, as shown in FIG. 5B, when an electric field is inducedbetween the first and the second patterned electrodes 330 a and 330 b bya voltage source 350, first portions 300 a of the liquid crystal 300between the first and second patterned electrodes 330 a and 330 brealign such that the liquid crystal molecules of the first portions areperpendicular to the substrates. In second portions 300 b adjacent thefirst portions 300 a the liquid crystal molecule maintain the firstordered molecular alignment. Therefore, under the influence of theelectric field, the first and the second portions 300 a and 300 b of theliquid crystal 300 attain different alignments. Such alignments havedifferent refractive indexes. Thus, the transmission of incident lightthrough the light valve can be controlled according to differences inthe refractive indexes of the first and second portions of the liquidcrystal.

[0031] The liquid crystal beneficially has a fast response time toenable the processing of a large quantity of image data, especially thatof moving images. However, in the nematic or the cholesteric liquidcrystal, the time required for the molecules to realigned under theinfluence of the electric field are too long, and consequently theresponse time of the liquid crystal is not fast enough for manyapplications.

[0032] Because of such limitation, a ferroelectric liquid crystal (FLC)in the smetic phase has become of interest. The FLC has a hundred timesfaster response time than the TN LC or the STN LC. This is because theFLC has a spontaneous polarization and a bistability that leads tohigh-speed responses, and thus an improvement in the imaging of movingimages. The high speed response of the FLC also improves the operationof a mouse used as an input device in computers, and the operation ofwindow operating systems.

[0033]FIG. 6 shows molecular alignments of the FLC. As shown, thelongitudinal axes of the liquid crystal molecules gradually align alonga helical structure.

[0034] To adapt the ferroelectric LC for liquid crystal displayapplications, the cell gap between the two transparent substrates of aliquid crystal display device should be uniformly maintained at lessthan about 2 micrometers. However, as shown in FIG. 7, a ferroelectricLC changes phase according to temperature. When compared with a smetic A(SmA) phase at high temperature, lower temperature phases smetic C_(A)*(SmC_(A)*) and smetic C* (SmC*) have the longitudinal axes of theirmolecules tilted at a tilt angle “E” with respect to a line that isperpendicular to the substrates (not shown).

[0035] Therefore, the molecular layer thickness “d2” of the smetic CA*(SmCA*) phase or the smetic C* (SmC*) phase is less than the molecularlayer thickness “d1” of the SmA phase. These thickness differencesbetween the phases of a ferroelectric LC cause difficulty in maintaininga uniform layer spacing.

[0036] Further, since the molecular layers of the SmA phase are moreordered than those of the Sm C_(A)* phase or of the SmC* phase, themolecules of the SmA phase are relatively easily aligned with analigning treatment. Therefore, to control the early state of themolecular alignment in the Sm C_(A)* or SmC* phase, the molecules areconventionally aligned in the SmA phase.

[0037] However, after the molecules are aligned in the SmA phase, as thephase of the FLC changes to the SmC_(A)* phase or to the SmC phase, themolecular alignments become more disordered due to the molecular layerthickness (d1, d2) difference between the phases. That is to say, as thephase changes from the SmA to the SmC_(A)* or SmC* phase, the moleculestilt to a definite angle, and the molecular layers space with gapsbetween themselves such that the molecular alignments are disordered.Additionally, the high temperature SmA phase has a lower transmittancethan the lower temperature SmC_(A) and SmC phase. A lower transmittanceresults in a low luminance of the liquid crystal display panel.

SUMMARY OF THE INVENTION

[0038] Accordingly, the principles of the present invention relate toliquid crystal panels that are designed to substantially obviate one ormore of the problems due to the limitations and disadvantages of therelated art.

[0039] It is an object of the present invention to provide a liquidcrystal display panel having a fast response time.

[0040] It is another object of the present invention to provide a methodfor fabricating diffraction gratings having a fast response time.

[0041] It is another object of the present invention to provide a liquidcrystal projector that uses a ferroelectric liquid crystal, beneficiallyone having reduced temperature dependence.

[0042] Additional features and advantages of the invention will be setforth in the description that follows, and in part will be apparent fromthe description, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

[0043] The principles of the present invention provide for a method offabricating a liquid crystal display device. Those principles includeforming a first orientation film on a first substrate, forming a secondorientation film on a second substrate, spacing the first and secondsubstrates apart, and interposing a ferroelectric liquid crystal layerbetween the first and second substrates. The ferroelectric liquidcrystal layer includes additives. Beneficially, the ferroelectric liquidcrystal layer is aligned by inducing a direct electric field to theferroelectric liquid crystal layer over and around a phase transitiontemperature of a SmC* phase. The additives form polymer networks,beneficially after exposing the ferroelectric liquid crystal layer tolight.

[0044] In an embodiment of the present invention the additives include amonoacrylate compound and/or a diacrylate compound. Ultraviolet light isa particularly useful way to form the polymer networks.

[0045] The principles of the present invention also provide for a methodof fabricating a diffraction grating of the types used liquid crystalcells. Such a method includes locating a ferroelectric liquid crystallayer having additives between first and second substrates. Then,forming a plurality of first and second grating portions in the liquidcrystal cell and then applying a first electric field to the firstgrating portions at a temperature near a phase transition temperature ofa SmC* phase. The first grating portion is then exposed to light using amask such that the ferroelectric liquid crystal layer is stabilized. Asecond electric field is then applied to the second grating portions ata temperature near a phase transition temperature of the SmC* phase. Thesecond grating portions are then exposed to light using a mask such thatthe ferroelectric liquid crystal layer is stabilized. Beneficially, theadditive includes a monoacrylate compound and/or a diacrylate compound.Furthermore, the alignment direction of the ferroelectric liquid crystallayer in the first grating portion is opposite to the alignmentdirection of the ferroelectric liquid crystal layer in the secondgrating portion. Beneficially, the first electric field is opposite tothe second electric field. Additionally, using ultraviolet light toexpose the grating portions is particularly useful.

[0046] The principles of the present invention also provide for a liquidcrystal projector for producing an image on an imaging screen. Thatprojector includes a light source, a plurality of light valves, and afocusing lens for collimating and focusing light from the light valves.Each light valve includes first and second substrates and aferroelectric liquid crystal layer between those substrates. Eachferroelectric liquid crystal layer is divided into first and secondportions that have different alignment orientations. First and secondtransparent conductive layers are located on the first and secondsubstrates.

[0047] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory and are intended to provide further explanation of theinvention as claimed.

BRIEF DESCRIPTION OF THE DRAWING

[0048] The accompanying drawings, which are included to provide afurther understanding of the invention and are incorporated in andconstitute a part of this specification, illustrate embodiments of theinvention and together with the description serve to explain theprinciples of the invention.

[0049] In the drawings:

[0050]FIG. 1 is a cross-sectional view of a typical TFT liquid crystaldisplay panel;

[0051]FIGS. 2A, 2B, and 2C illustrate molecular alignments of nematic,smetic, and cholesteric liquid crystals, respectively;

[0052]FIGS. 3A and 3B illustrate a configuration and an operation of aliquid crystal panel;

[0053]FIG. 4 schematically illustrates a liquid crystal projector;

[0054]FIGS. 5A and 5B illustrate the operation of a light valve;

[0055]FIG. 6 shows molecular alignments of the FLC;

[0056]FIG. 7 shows phase changes of the FLC according to varioustemperatures;

[0057]FIGS. 8A and 8B show a method of aligning the FLC according to anembodiment of the present invention;

[0058]FIG. 9 illustrates a polymer network formed by light;

[0059]FIGS. 10A and 10B illustrate a forming of a diffraction gratingaccording to an embodiment of the present invention;

[0060]FIG. 11 illustrates the operation of the diffraction grating shownin FIG. 10B; and

[0061]FIG. 12 illustrates a liquid crystal projector according to anembodiment of the present invention.

DETAILED DESCRIPTION OF AN ILLUSTRATED EMBODIMENT

[0062] Reference will now be made in detail to an embodiment of thepresent invention, an example of which is illustrated in theaccompanying drawings.

[0063]FIGS. 8A, 8B, and 11 help illustrate a method of fabricating aliquid crystal panel according to the principles of the presentinvention.

[0064] As shown in FIGS. 8A and 8B, a FLC 500 is interposed betweenfirst and second substrates 400 and 402. A voltage source 450 applies anelectric field to the FLC via electrodes (not shown) on the first andsecond substrates. The FLC 500 is mixed with a polymerizing additive oradditives. Beneficially, that additive includes a monoacrylate compoundand/or a diacrylate compound that can be light polymerized. The firstand second substrates are preferably comprised of a transparent materialsuch as a glass.

[0065] Though not shown in FIGS. 8A, 8B, and 11, but as shown FIGS. 3Aand 3B, on opposing surfaces of the first and second substrates arefirst and second orientation films. Those films beneficially have firstand second rubbing directions, respectively.

[0066] The voltage source 450 induces the electric field to the FLC 500when the temperature of the FLC is below the phase transition from theSmA phase to the SmC* phase. Under such conditions, the liquid crystalmolecules of the FLC 500 are tilted to a definite angle relative to thenormal direction of the layer. Before the electric field is applied,since the temperature is over the phase transition point of the SmCphase, the liquid crystal molecules were substantially aligned in theSmC phase as shown in FIG. 7. The electric field of FIG. 8B is oppositethat in FIG. 8A. The result is that the liquid crystal molecules of FIG.8B are tilted in an opposite direction

[0067]FIGS. 10A and 10B illustrate the liquid crystal cell describedabove adapted for use in a light valve diffraction grating 700 of thetype used in a liquid crystal projector. As shown, in the diffractiongrating 700 the FLC 500 is interposed between the first and secondsubstrates 400 and 402. Above the second substrate 402 is a mask 600having transparent portions 600 a and opaque portions 600 b. Thetransparent portions 600 a transmit almost all incident light, while theopaque portion 600 b reflects or absorbs almost all incident light. TheFLC 500 is mixed with an additive, beneficially an additive as mentionedabove. First and second grating portions 500 a and 500 b within the FLCrespectively correspond to the transparent and opaque portions 600 a and600 b of the mask 600. Each of the first and second portions 500 a and500 b of the FLC 500 beneficially has a width of “L.”

[0068] Similar to FIG. 8A, a voltage source 450 applies an electricfield to the FLC 500 when the temperature is over the phase transitiontemperature of the SmC* phase.

[0069] Under the incident light, only the transparent portions 600 a ofthe mask 600 transmit light. That transmitted light is applied to thefirst grating portions 500 a of the FLC 500. The opaque portions 600 bof the mask 600 shield the second grating portion 500 b of the FLC 500from the incident light.

[0070] The additives in the first grating portions 500 a of the FLC arepolymerized by the incident light. This is illustrated in FIG. 9, whichshows polymer networks 404 being formed in a first grating portion 500a. After the polymer networks 404 are formed, the incident light and theelectric field are stopped. The liquid crystal layers of the firstgrating portions are then formed according the electric field. That is,the additives form polymer networks 404 that are aligned along thealignment directions of the liquid crystal layer when that layer isunder the influence of the electric field.

[0071] Turning now to FIG. 100B, the mask 600 is then moved parallel tothe substrates such that the transparent portions 600 a of the mask 600align with the second grating portions 500 b of the FLC 500. The voltagesource 450 then induces an opposite electric field across the FLC 500.Incident light then forms polymer networks from the additives added tothe FLC in the second grating portions 500 b. Those polymer networksstabilize opposite to the first grating portion 500 a. At this point,although the polymer networks in the first grating portion 500 a aresubstantially stabilized, the opposite electric field could affect themolecular orientation of the first grating portion 500 a. Therefore, asshown in FIG. 10B, the opaque portions 600 b of the mask 600beneficially shield the first grating portions 500 a when light isapplied to the second grating portions.

[0072] Through the above-mentioned fabricating method, the first andsecond grating portions 500 a and 500 b are stabilized in oppositeorientations. The result is a diffraction grating 700 that is in accordwith the principles of the present invention. Due to the polymernetworks, that diffraction grating tends to maintain its FLC molecularlayer structure regardless of temperature.

[0073] With reference to FIG. 11, the operation of the diffractiongrating 700 will now be explained. As shown, incident light 800 havingan incidence angle of “0” is applied to the FLC layer 500 of thediffraction grating 700. The incident light 800 is then divided into adiffracted light 802 having a diffraction angle of “(p” and atransmitted light 804 having the same transmittance angle of “0” as theincidence angle. The incident, diffracted, and transmitted light 800,802, and 804 respectively have first, second, and third brightness“I_(in)”, “I_(d)”, and “I_(t)”. The FLC layer 500 has a molecular layerthickness of “d”, and the first and second grating portions 500 a and500 b respectively have first and second refractive indexes “n₁” and“n₂”. Furthermore, each of the first and second grating portions 500 aand 500 b of the FLC layer 500 has a width of “L.”

[0074] The second brightness I_(d) (of the diffracted light 802) dependson the incidence angle θ, the molecular layer thickness d, the width L,the first and second refractive indexes n₁ and n₂, and the diffractionangle φ. Furthermore, since the first and second refractive indexes n₁and n₂ vary according to the electric field applied to the FLC layer,the second brightness I_(d) of the diffracted light 802 can becontrolled by that electric field.

[0075]FIG. 12 illustrates the operation of a liquid crystal projectorthat is in accord with the principles of the present invention. Asshown, spaced apart at a proper angle and distance from the diffractiongrating 700 is a focusing lens 240. The lens 240 directs light onto animage screen 250. As the incident light 800 from a light source 900passes through the diffraction grating 700 at a proper incidence angle,the incident light 800 divides into the diffracted and transmitted light802 and 804 in accord with the electric field applied to the FLC (notshown) of the diffraction grating 700.

[0076] The focusing lens 240 concentrates rays of the diffracted light802 into focus on the image screen 250 such that images are displayed.As explained above with reference to FIG. 11, the brightness of thediffracted light 802 is controlled by the electric field induced in theFLC of the diffraction grating 700. That is to say, as the inducedelectric field varies, the brightness of the refracted light changessuch that a gray scale rendering can be achieved.

[0077] The diffraction grating 700 of FIG. 12 includes not only thefirst and second substrates 400 and 402 (see, for example, FIG. 9), butin this case of acting has a light valve, the first and second substrate400 and 402 include transparent conductive layers 810 and 812,respectively (see FIG. 11).

[0078] A diffraction grating according to the principles of the presentinvention uses the FLC to achieve high speed responses and a superiorimage quality, particularly when displaying moving images.

[0079] Further, using an FLC mixed with an additive, such as amonoacrylate and/or a diacrylate compound, to produce polymer networksenables a stable brightness regardless of the temperature. Beneficially,only a small quantity of the additive is mixed in the FLC. This preventssignificant changes in the electrical and chemical properties of theFLC. It also allows the polymer networks to be formed using light toinduce polymerization. The polymer networks connect with each otheracross the molecular layers in the FLC such that the molecules of theFLC are stabilized in a proper orientation and to maintain theirmolecular layer structure over temperature changes. Accordingly, thebrightness of the diffraction grating is stabled with regards totemperature. Additionally, the polymer networks improve the ruggednessof the FLC layer by reducing damage caused by external impacts.

[0080] While the principles of the present invention has beenillustrated and described with reference to an embodiment thereof, itwill be understood by those skilled in the art that the changes in formand details may be made without departing from the spirit and scope ofthe invention. Thus, it is intended that the present invention coversthe modifications and variations that come within the scope of theappended claims or their equivalents.

What is claimed is:
 1. A method of fabricating a liquid crystal displaydevice, comprising: forming a first orientation film on a firstsubstrate; forming a second orientation film on a second substrate;spacing the first and second substrates apart by a gap; adding anadditive to a ferroelectric liquid crystal; inserting the ferroelectricliquid crystal with the additive in the gap; aligning the ferroelectricliquid crystal by inducing an electric field across the ferroelectricliquid crystal over a phase transition temperature of a SmC* phase; andforming polymer networks in the ferroelectric liquid by polymerizing theadditive.
 2. A method of fabricating a liquid crystal display deviceaccording to claim 1, wherein the additive includes a monoacrylatecompound.
 3. A method of fabricating a liquid crystal display deviceaccording to claim 1, wherein the additive includes a diacrylatecompound.
 4. A method of fabricating a liquid crystal display deviceaccording to claim 1, wherein the polymer networks are formed byexposing the ferroelectric liquid to light.
 5. A method of fabricating aliquid crystal display device according to claim 1, wherein the exposinglight is ultraviolet.
 6. A method of fabricating a diffraction grating,comprising: adding an additive to a ferroelectric liquid crystal;inserting the ferroelectric liquid crystal having the additive betweenfirst and second substrates; forming a plurality of first gratingportions by producing a plurality of first polymer networks in theferroelectric liquid crystal; and forming a plurality of second gratingportions by producing a plurality of second polymer networks in theferroelectric liquid crystal.
 7. A method of fabricating a diffractiongrating according to claim 6, wherein the first grating portions areproduced by: illuminating first portions of the ferroelectric liquidcrystal with light; applying a first electric field having a firstdirection across the first portions; and maintaining the temperature ofthe ferroelectric liquid crystal above a phase transition temperature ofa SmC* phase.
 8. A method of fabricating a diffraction grating accordingto claim 7, wherein the first portions are illuminated through a mask.9. A method of fabricating a diffraction grating according to claim 7,wherein the illuminating light is ultraviolet.
 10. A method offabricating a diffraction grating according to claim 6, wherein theadditive includes a monoacrylate compound.
 11. A method of fabricating adiffraction grating according to claim 6, wherein the additive includesa diacrylate compound.
 12. A method of fabricating a diffraction gratingaccording to claim 7, wherein the second grating portions are producedby: illuminating second portions of the ferroelectric liquid crystalwith light; applying a second electric field having a second directionacross the second portions; and maintaining the temperature of theferroelectric liquid crystal above a phase transition temperature of aSmC* phase.
 13. A method of fabricating a diffraction grating accordingto claim 12, wherein second direction is opposite to the firstdirection.
 14. A method of fabricating a diffraction grating accordingto claim 12, wherein an alignment direction of the ferroelectric liquidcrystal layer in the first grating portions is opposite to an alignmentdirection of the ferroelectric liquid crystal layer in the secondgrating portions.
 15. A liquid crystal projector, comprising: a lightsource for producing light; a plurality of light valves for selectivelytransmitting said light, each of said plurality of light valvesincluding a first substrate, a second substrate, and an interposedferroelectric liquid crystal layer; and a focusing lens for focusingsaid transmitted light from said plurality of light valves onto ascreen.
 16. A liquid crystal projector according to claim 15, furtherincluding: a red dichroic mirror for directing a red portion of saidlight to a first of said plurality of light valves; and a green dichroicmirror for directing a green portion of said light to a second of saidplurality of light valves.
 17. A liquid crystal projector according toclaim 15, wherein said interposed ferroelectric liquid crystal layer ofeach of said plurality of light valves includes a plurality of firstgrating portions and a plurality of second grating portions, whereinsaid first and second grating portions have different alignmentorientations.
 18. A liquid crystal projector according to claim 17,wherein said first grating portions include polymer networks.
 19. Aliquid crystal projector according to claim 18, wherein said polymernetworks are a polymerized monoacrylate compound.
 20. A liquid crystalprojector according to claim 18, wherein said polymer networks are apolymerized diacrylate compound.
 21. A liquid crystal projectoraccording to claim 15, wherein each of said plurality of light valvesincludes first and second transparent conductive layers on said firstand second substrates.
 22. A liquid crystal projector according to claim15, further including an image screen for receiving focused light fromsaid focusing lens.